Cleanup app snapshots on isolate/vm exit.

runtime/bin/file_fuchsia.cc

Index: runtime/bin/file_fuchsia.cc
diff --git a/runtime/bin/file_fuchsia.cc b/runtime/bin/file_fuchsia.cc
index 19595953a8cc17f30127a20f710987753ca0b54f..b18f4237177103f148d7b7ef4e10675c1cf10d04 100644
--- a/runtime/bin/file_fuchsia.cc
+++ b/runtime/bin/file_fuchsia.cc
@@ -77,12 +77,17 @@ bool File::IsClosed() {
 }
 
 
-void* File::Map(MapType type, int64_t position, int64_t length) {
+MappedMemory* File::Map(MapType type, int64_t position, int64_t length) {
   UNIMPLEMENTED();
   return NULL;
 }
 
 
+void MappedMemory::Unmap() {
+  UNIMPLEMENTED();
+}
+
+
 int64_t File::Read(void* buffer, int64_t num_bytes) {
   ASSERT(handle_->fd() >= 0);
   return NO_RETRY_EXPECTED(read(handle_->fd(), buffer, num_bytes));